1. Field of the Invention
The present invention relates to an optical disc apparatus capable of recording information onto lands and grooves, which are formed on an optical disc, respectively, or capable of reproducing recorded information, respectively, and relates to a land/groove detecting circuit. Particularly, the present invention relates to an optical disc apparatus, which appropriately detects the lands and grooves, making it possible to stably perform track pull-in operations with respect to the lands and grooves, respectively, and relates to a land/groove detecting circuit.
2. Description of the Related Art
In generally, the optical disc comprises groove portions, which are referred to as grooves, and land portions, which are referred to as lands, such that they are helically or concentrically provided in a row arrangement alternately. The conventional optical disc apparatus records or reproduces information using either the lands or the grooves.
In recent years, to improve recording density of the optical disc, there has been known an optical disc apparatus, which employs a land/groove recording and reproducing system in which information can be recorded in the lands and the grooves and reproduced. FIG. 16 is a block diagram showing one example of the conventional optical disc apparatus using the land/groove recording and reproducing system.
As shown in FIG. 16, the optical disc apparatus comprises an optical head 101, a thread motor 121, a focus control system 300, and a track control system 310.
The optical head 101 comprises a laser 102, an objective lens 120, a beam splitter 103, an optical sensor 104, a focus actuator 105, and a track actuator 106, and records information onto the lands and grooves of the optical disc 100, which is driven at a given number of revolutions by a spindle motor (not shown), and reproduces information stored therein, respectively.
The laser 102 generates optical beams (laser beams), and irradiates the optical disc 100 through the objective lens 120. The objective lens 120 converges the optical beams onto a track surface of the optical disc 100 (where the lands and grooves are formed) to be irradiated therewith. Also, the object lens 120 sends the reflected light of optical beams to the optical sensor 104, and forms an image on the optical sensor 104 through the beam splitter 103. The beam splitter 103 changes an optical path of the reflected light from the optical disc 100, and supplies the reflected light to the optical sensor 104. The optical sensor 104 has four light-receiving sections, generates a servo signal in accordance with the amount of light received by the respective light-receiving sections, and supplies the generated servo signal to the focus control system 300 and the track control system 310.
The focus actuator 105, which is controlled by the focus control system 300, moves the objective lens 120 along an optical axis (focus direction). The track actuator 106, which is controlled by the track control system 310, moves the objective lens 120 in the direction of the radius of the optical disc 100 (tracking direction). In other words, the track actuator 106 controls the objective lens 120 such that the optical beams with which the optical disc 100 is irradiated are rendered to follow the target lands or grooves.
The thread motor 121 moves the entirety of the optical head 101 in the radial direction of the optical disc 100.
The focus control system 300 comprises a focus error signal generating circuit 107, a phase compensation filter 109, a switch circuit 125, a driver amplifier 122, and a CPU 124, and controls the focus actuator 105.
The focus error signal generating circuit 107 generates a focus error signal 108, which shows the shift of the optical beams, with which the optical disc 100 has been irradiated, from the focal point of the disc surface, in accordance with the servo signal. The phase compensation filter 109 supplies the focus error signal 108 to the driver amplifier 122 through the switch circuit 125 as compensating for its phase. The switch circuit 125, which is controlled by CPU 124, turns on or off the entire operation of the focus control system 300. The driver amplifier 122 drives the focus actuator 105 such that the value of the supplied focus error signal 108 becomes xe2x80x9c0xe2x80x9d.
The track control system 310 comprises a track error signal generating circuit 110, a phase compensation filter 112, a switch circuit 126, a driver amplifier 123, and a CPU 124, and controls the track actuator 106.
The track error generating circuit 110 generates a track error signal 111, which shows the shift of the optical beams, with which the optical disc 100 has been irradiated, from the track (the center of the lands or grooves), in accordance with the servo signal. The phase compensation filter 112 supplies the track error signal 111 to the driver amplifier 123 through the switch circuit 126 as compensating for its phase. The switch circuit 126, which is controlled by CPU 124, turns on or off the entire operation of the track control system 310. The driver amplifier 123 drives the focus actuator 106 such that the value of the supplied track error signal 111 becomes xe2x80x9c0xe2x80x9d.
The CPU 124 performs on/off control of the entire operation of each of the focus control system 300 and the track control system 310 by controlling the switching circuits 125 and 126.
The following will specifically explain the track error signal 111, which is generated when the optical beams irradiated from the optical head 101 move on the optical disc 100, with reference to FIG. 17.
If the optical beams irradiated from the optical head 101 move on the rotating optical disc 100 in the radial direction, the actual track is shown by an arrow LB of FIG. 17A. In other words, the optical beams pass through the lands and grooves as crossing them sequentially along the arrow LB and they pass through the headers on the way. Since the reflection state of optical beams changes at the time of these passages, the amount of received light of each light receiving sections of the optical sensor 104, which receives the reflected light, also changes. The signal level of the track error signal 111 generated by the track error signal generating circuit 107 changes with the above change.
More specifically, as shown FIG. 17B, if the optical beams move on the optical disc 100, the signal level of the track error signal 111 becomes xe2x80x9c0xe2x80x9d when the optical beams are present at the centers P1, P3, P5 of the lands and grooves. Then, if the optical beams deviate from these centers, the signal level changes to a positive side or a negative side.
For this reason, the track control system 310 provides feedback control to the track actuator 106 such that the signal level of the track error signal 111 becomes xe2x80x9c0xe2x80x9d, rendering the optical beams irradiated from the optical head 101 to follow the centers of the target lands or those of the grooves.
The polarity of the track error signal 111 differs between a case in which the optical beams move from the land to the groove and a case in which the optical beams move from the groove to the land. For this reason, in a track pull-in operation in which the optical beams are rendered to follow the target track (lands or grooves), in some cases, the optical disc apparatus has difficulty in performing the track pull-in operation stably. In other words, if the track actuator 106 is controlled with the polarity opposite to the actual case, the track control system 310 is subjected to a positive feedback (the signal level is not changed to xe2x80x9c0xe2x80x9d).
Therefore, when the track control system 310 controls the track actuator 106, the polarity of the track error signal 111 must be inverted in a case in which the optical beams are rendered to follow the lands and a case in which the optical beams are rendered to follow the grooves.
Unexamined Japanese Patent Application KOKAI Publication No. H5-109093 discloses the technique in which the polarities of the lands and grooves are detected when the track pull-in operation is performed. While, Examined Japanese Patent Application KOKOKU Publication Nos. S63-4271 and H1-54794 disclose the technique in which the track pull-in operation can be stably performed even when the track actuator is controlled with the opposite polarity.
The optical disc apparatus disclosed in Unexamined Japanese Patent Application KOKAI Publication No. H5-109093 binarizes a track sum signal, which shows the total amount of received light, in accordance with the difference in the reflection coefficient of the optical beams between the lands and the grooves, thereby determining the polarity of the land or that of the groove. The optical disc apparatus performs the track pull-in operation when the determined polarity of the land or that of the groove matches a reference polarity. As a result, the track pull-in operation can be stably performed.
While, the optical disc apparatus disclosed in Examined Japanese Patent Application KOKOKU Publication Nos. S63-4271 and H1-54794 make use of the point that an envelope component of a RF signal of such as FM signal band, etc., which is recorded in the optical disc is out of shift with the track error signal 90 degrees. The optical disc apparatus binarizes the envelope component of RF signal and the track error signal individually. The optical disc apparatus samples the envelope component of the binarized RF signal at the time of detecting an edge of the binarized track error signal. The optical disc apparatus generates a track error signal as holding the sampled value until a next edge of the track error signal is detected. At the time of performing the track control in accordance with the generated track gate signal, the optical disc apparatus makes the track control valid only when the polarity of the specified land or the groove matches the polarity of the track gate signal. As a result, the track pull-in operation can be stably performed.
However, the techniques disclosed in these publications are directed to the case in which information is recorded onto either the lands or the grooves. This makes it difficult to detect the polarities of the lands and grooves appropriately even if these techniques are directly applied to the optical disc apparatus of the land/groove recording and reproducing system. Namely, the reflection coefficient of the land and that of the groove are preferably equal to each other in the actual optical disc of the land/groove recording and reproducing system. This results in that the detection method using the difference in the reflection coefficient on the disc as disclosed in Unexamined Japanese Patent Application KOKAI Publication No. H5-109093 can not be used. Also, the envelope of the RF signal cannot be obtained in an unrecorded state of information at the time of an initial use of the optical disc. This results in that the method using the envelope of the RF signal disclosed in Examined Japanese Patent Application KOKOKU Publication Nos. S63-4271 and H1-54794 can not be used.
In a case where the optical disc apparatus of the land/groove recording and reproducing system can not detect the polarities of the land and groove, the track pull-in operation becomes unstable. Namely, if the polarities of the land and groove can not be detected correctly, the probability that the polarity of the target land or the groove will match the polarity of the land or the groove, which the optical beams are presently following, reduces to xc2xd at the time of the track pull-in operation. Then, in a case where the track pull-in operation is performed with the polarity opposite to the original polarity, the track control system is subjected to the positive feedback, and the track actuator, etc., may run way.
In order to solve the above problems, Unexamined Japanese Patent Application KOKAI Publication No. H9-305985 discloses the technique of determining the lands and grooves. This technique makes use of inverting the relationship in the phase between a vibration waveform obtained when the track actuator is vibrated at a predetermined frequency and the signal waveform of the track error signal in the lands and grooves. The optical disc apparatus disclosed in Unexamined Japanese Patent Application KOKAI Publication No. H9-305985 vibrates the track actuator in the radial direction of the optical disc at a relatively high frequency within the range of less than xc2xc of the distance between adjacent lands. The optical disc apparatus determines the lands and grooves from the relationship in the phase between the vibration waveform and the signal waveform occurring at the track error signal, and performs the track pull-in operation. As a result, the lands and the grooves can be determined.
However, in the technique disclosed in Unexamined Japanese Patent Application KOKAI Publication No. H9-305985, there is a possibility that the detection of the lands and grooves will become difficult in the actual optical disc. The optical disc apparatus disclosed in Unexamined Japanese Patent Application KOKAI Publication No. H9-305985 vibrates the track actuator in the radial direction of the optical disc so as to obtain the signal for a polarity determination. In this case, since eccentricity, that is, the shift between the center of the disc and that of the rotation exists in the actual optical disc, there is a case in which an error signal, which is caused with the periodic relative displacement, is not output to the track actuator in accordance with the rotation of the optical disc. As a result, it is impossible to clearly differentiate between the error signal and the signal for a polarity determination. For this reason, the detection of the lands and grooves cannot be accurately performed only by the technique disclosed in Unexamined Japanese Patent Application KOKAI Publication No. H9-305985. Moreover, since the track pull-in operation is performed in a state in which the track actuator vibrates, an amount of control increases to some extent. This causes possibility that the optical beams will rush into the track with the opposite polarity over the target track (lands and grooves). Then, if the track pull-in operation is performed with the opposite polarity, the probability that a failure will occur in the pull-in operation increases, and it becomes necessary to perform the track pull-in operation again, with the result that much time is required for the sequence of the track pull-in.
An object of the present invention is to provide an optical disc apparatus capable of appropriately determining polarities of lands and grooves and capable of performing a track pull-in operation stably, and to provide a land/groove detecting circuit. Also, another object of the present invention is to provide an optical disc apparatus, which can shorten track pull-in time and seek operation time by stabilizing a track pull-in operation, and to provide a land/groove detecting circuit.
In order to the above objects, according to the first aspect of the present invention, there is provided an optical disc apparatus comprising optical beam irradiating means for irradiating a track, which has lands and grooves formed on an optical disc, with optical beams; light-receiving means for receiving reflected light of the optical beams irradiated by the optical beam irradiating means; track error signal generating means for generating a track error signal, which shows a shift from the track in the optical beam irradiated by the optical beam irradiating means, in accordance with an amount of the reflected light received by the light receiving means; track sum signal generating means for generating a track sum signal, which shows a total amount of the reflected light, in accordance with the amount of the reflected light received by the light receiving means; land/groove detecting means for generating a track pull-in enabling signal, which shows track pull-in enabling timing, and a land/groove detection signal for determining a land or a groove in accordance with the track error signal generated by the track error signal generating means and the track sum signal generated by the track sum signal generating means; and track pull-in means for performing track pull-in in accordance with the track pull-in enabling signal generated by the land/groove detecting means and the land/groove detection signal.
According to this invention, the track error signal generating means generates the track error signal, which shows the shift from the track in the optical beams irradiated by the optical beam irradiating means, in accordance with the amount of reflected light received by the light receiving means. The track sum signal generating means generates the track sum signal, which shows the total amount of reflected light, in accordance with the amount of reflected light received by the light receiving means. The land/groove detecting means generates the land/groove detection signal for determining the track pull-in enabling signal, which shows the track pull-in enabling timing, and the land or the groove detection signal in accordance with the track error signal generated by the track error signal generating means and the track sum signal generated by the track sum signal generating means. As a result, the polarity of the land and that of the groove can be appropriately determined, so that the track pull-in operation can be stably operated. Also, it is possible to shorten track pull-in time and seek operation time by stabilizing the track pull-in operation.
The land/groove detecting means may comprise header area signal generating means for generating a header area signal, which shows a header area in the optical disc, in accordance with the track sum signal generated by the track sum signal generating means; track pull-in enabling signal generating means for generating the track pull-in enabling signal in accordance with the track error signal generated by the track error signal generating means and the header area signal generated by the header area signal generating means; track cross signal generating means for generating a track cross signal, which shows that the optical beams irradiated by the optical beam irradiating means have crossed the center of the track; and land/groove detection signal generating means for generating a land/groove detection signal in accordance with the track pull-in enabling signal generated by the track pull-in enabling signal generating means, the header area signal generated by the header area signal generating means, and the track cross signal generated by the track cross signal generating means. In this case, not only the track pull-in enabling timing but also the polarity of the land and that of the groove can be appropriately determined.
The header area signal generating means may comprise a peak detector for detecting a peak value from the track sum signal generated by the track sum signal generating means; a low-pass filter for extracting a low frequency component from the track sum signal generated by the track sum signal generating means; a header detection level generator for generating a header detection level in accordance with the peak value detected by the peak detector and the low frequency component extracted by the low-pass filter; and a header area detector for comparing the track sum signal generated by the track sum signal generating means with the header detection level generated by the header detection level generator so as to generate the header area signal.
The track pull-in enabling signal generating means may comprise a level comparator for comparing the track error signal generated by the track error signal generating means with each of a predetermined upper limit level and a predetermined lower limit level so as to generate two comparison signals showing the comparison results; a logic unit for ANDing two comparison signals generated by the level comparator; and a header component removal arithmetic unit for outputting the track pull-in enabling signal from which the header component is removed from the result of the logic unit in accordance with the header area signal generated by the header area signal generating means.
The track pull-in enabling signal detecting means may comprise an absolute value signal generator for generating an absolute value signal in which a negative level is inverted from the track error signal generated by the track error signal generating means; a defined level comparator for comparing the absolute value signal generated by the absolute value signal generator with a predetermined defined level so as to generate a comparison signal showing the comparison result; and a header component removal arithmetic unit for outputting the track pull-in enabling signal from which the header component is removed from the comparison signal generated by the defined level comparator in accordance with the header area signal generated by the header area signal generating means.
The track pull-in enabling signal detecting means may comprise a low-pass filter for extracting a low frequency component from the track error signal generated by the track error signal generating means; a level comparator for comparing the low frequency component extracted by the low-pass filter with each of a predetermined upper limit level and a predetermined lower limit level so as to generate two comparison signals showing the comparison results; and a logic unit for ANDing two comparison signals generated by the level comparator.
The track pull-in enabling signal detecting means may comprise a low-pass filter for extracting a low frequency component from the track error signal generated by the track error signal generating means; an absolute value signal generator for generating an absolute value signal in which a negative level is inverted from the low frequency component extracted by the low-pass filter; and a defined level comparator for comparing the absolute value signal generated by the absolute value signal generator with a predetermined defined level so as to generate a comparison signal showing the comparison result.
The land/groove detection signal generating means may comprise a track polarity inverter for generating a land/groove detection signal in which a signal level in the land and groove is inverted in accordance with the track pull-in enabling signal generated by the track pull-in enabling signal generating means; a sample holder for holding a signal level of the track cross signal generated by the track cross signal generating means in accordance with the header area signal generated by the header area signal generating means; and a track polarity corrector for inverting the signal level of the land/groove detection signal generated by the track polarity inverter when the land/groove detection signal generated by the track polarity inverter is compared with the track cross signal held by the sample holder and no match exists in both signals.
The land/groove detection signal generating means may further comprise means for inputting a land/groove selection signal, which selects either one of the land and the groove, and for outputting a signal enabling a target track pull-in to be performed in accordance with the input land/groove selection signal.
In order to achieve the above objects, according to the second aspect of the present invention, there is provided an optical disc apparatus comprising a laser irradiator for irradiating a track, which has a land and a groove formed on an optical disc, with optical beams; an optical sensor for receiving reflected light of the optical beams irradiated by the laser irradiator; a track error signal generating circuit for generating a track error signal, which shows a shift from the track in the optical beam irradiated by the laser irradiator, in accordance with an amount of the reflected light received by the optical sensor; a track sum signal generating circuit for generating a track sum signal, which shows a total amount of the reflected light, in accordance with the amount of the reflected light received by the optical sensor; a land/groove detecting circuit for generating a track pull-in enabling signal, which shows track pull-in enabling timing, and a land/groove detection signal for determining a land or a groove in accordance with the track error signal generated by the track error signal generating circuit and the track sum signal generated by the track sum signal generating circuit; and a track actuator for performing track pull-in in accordance with the track pull-in enabling signal generated by the land/groove detecting circuit and the land/groove detection signal.
According to this invention, the track error signal generating circuit generates the track error signal, which shows the shift from the track in the optical beams irradiated by the laser irradiator, in accordance with the amount of reflected light received by the optical sensor. The track sum signal generating circuit generates the track sum signal, which shows the total amount of reflected light, in accordance with the amount of reflected light received by the optical sensor. The land/groove detecting circuit generates the land/groove detection signal for determining the track pull-in enabling signal, which shows the track pull-in enabling timing, and the land or the groove detection signal in accordance with the track error signal generated by the track error signal generating circuit and the track sum signal generated by the track sum signal generating circuit. As a result, the polarity of the land and that of the groove can be appropriately determined, so that the track pull-in operation can be stably operated. Also, it is possible to shorten track pull-in time and seek operation time by stabilizing the track pull-in operation.
In order to achieve the above objects, according to the third aspect of the present invention, there is provided a land/groove detecting circuit comprising header area signal generating means for generating a header area signal, which shows a header area in an optical disc, in accordance with a track sum signal, which shows the total amount of reflected light of optical beams with which a track, which has lands and grooves formed on the optical disc, is irradiated; track pull-in enabling signal generating means for generating a track pull-in enabling signal, which shows track pull-in enabling timing, in accordance with a track error signal, which shows a shift from the track in the optical beams with which the optical disc is irradiated, a header area signal generated by the header area signal generating means; track cross signal generating means for generating a track cross signal, which shows that the optical beams with which the optical disc is irradiated have crossed the center of the track; and land/groove detection signal generating means for generating a land/groove detection signal for determining a land or a groove in accordance with the track pull-in enabling signal generated by the track pull-in enabling signal generating means, the header area signal generated by the header area signal generating means, and the track cross signal generated by the track cross signal generating means.
According to this invention, the header area signal generating means generates the header area signal, which shows the header area in the optical disk, in accordance with the track sum signal, which shows the total amount of reflected light of the optical beams with which the track, which has the land and the ground formed on the optical disc, is irradiated. The track pull-in enabling signal generating means generates the track pull-in enabling signal, which shows the track pull-in enabling timing, in accordance with the track error signal, which shows the shift from the track in the optical beams with which the optical disc is irradiated, the header area signal generated by the header area signal generating means. The track cross signal generating means generates the track cross signal, which shows that the optical beams with which the optical disc is irradiated have crossed the center of the track. The land/groove detection signal generating means generates the land/groove detection signal for determining a land or a groove in accordance with the track pull-in enabling signal generated by the track pull-in enabling signal generating means, the header area signal generated by the header area signal generating means, and the track cross signal generated by the track cross signal generating means. As a result, not only the track pull-in enabling timing but also the polarity of the land and that of the groove can be appropriately determined.
The header area signal generating means may comprise a peak detector for detecting a peak value from the track sum signal, which shows the total amount of reflected light of the optical beams with which the optical disk is irradiated; a low-pass filter for extracting a low frequency component from the track sum signal, which shows the total amount of reflected light of the optical beams with which the optical disk is irradiated; a header detection level generator for generating a header detection level in accordance with the peak value detected by the peak detector and the low frequency component extracted by the low-pass filter; and a header area detector for comparing the track sum signal, which shows the total amount of reflected light of the optical beams with which the optical disk is irradiated, with the header detection level generated by the header detection level generator so as to generate the header area signal.
The track pull-in enabling signal generating means may comprise a level comparator for comparing the track error signal, which shows a shift from the track in the optical beams with which the optical disc is irradiated, with each of a predetermined upper limit level and a predetermined lower limit level so as to generate two comparison signals showing the comparison results; a logic unit for ANDing two comparison signals generated by the level comparator; and a header component removal arithmetic unit for outputting the track pull-in enabling signal from which the header component is removed from the result of the logic unit in accordance with the header area signal generated by the header area signal generating means.
The track pull-in enabling signal detecting means may comprise: an absolute value signal generator for generating an absolute value signal in which a negative level is inverted from the track error signal generated by the track error signal, which shows a shift from the track in the optical beams with which the optical disc is irradiated; a defined level comparator for comparing the absolute value signal generated by the absolute value signal generator with a predetermined defined level so as to generate a comparison signal showing the comparison result; and a header component removal arithmetic unit for outputting the track pull-in enabling signal from which the header component is removed from the comparison signal generated by the defined level comparator in accordance with the header area signal generated by the header area signal generating means.
The track pull-in enabling detecting means may comprise: a low-pass filter for extracting a low frequency component from the track error signal, which shows a shift from the track in the optical beams with which the optical disc is irradiated; a level comparator for comparing the low frequency component extracted by the low-pass filter with each of predetermined upper limit level and lower limit level so as to generate two comparison signals showing the comparison result; and a logic unit for ANDing two comparison signals generated by the level comparator.
The track pull-in enabling signal detecting means may comprise: a low-pass filter for extracting a low frequency component from the track error signal, which shows a shift from the track in the optical beams with which the optical disc is irradiated; an absolute value signal generator for generating an absolute value signal in which a negative level is inverted from the low frequency component extracted by the low-pass filter; and a defined level comparator for comparing the absolute value signal generated by the absolute value signal generator with a predetermined defined level so as to generate a comparison signal showing the comparison result.
The land/groove detection signal generating means may comprise a track polarity inverter for generating a land/groove detection signal in which a signal level in the land and groove is inverted in accordance with the track pull-in enabling signal generated by the track pull-in enabling signal generating means; a sample holder for holding a signal level of the track cross signal generated by the rack cross signal generating means in accordance with the header area signal generated by the header area signal generating means; and a track polarity corrector for inverting the signal level of the land/groove detection signal generated by the track polarity inverter when the land/groove detection signal generated by the track polarity inverter is compared with the track cross signal held by the sample holder and no match exists in both signals.
The land/groove detecting circuit may further comprises means for inputting a land/groove selection signal, which selects either one of the land and the groove, and for outputting a signal enabling a target track pull-in to be performed in accordance with the input land/groove selection signal.
In order to achieve the above objects, according to the fourth aspect of the present invention, there is provided a land/groove detecting circuit comprising a header area signal generating circuit for generating a header area signal, which shows a header area in an optical disc, in accordance with a track sum signal, which shows a total amount of reflected light of optical beams with which a track, which has lands and grooves formed on the optical disc, is irradiated; a track pull-in enabling signal generating circuit for generating a track pull-in enabling signal, which shows track pull-in enabling timing, in accordance with a track error signal, which shows a shift from the track in the optical beams with which the optical disc is irradiated, a header area signal generated by the header area signal generating circuit; a track cross signal generating circuit for generating a track cross signal, which shows that the optical beams with which the optical disc is irradiated have crossed the center of the track; and a land/groove detection signal generating circuit for generating a land/groove detection signal for determining a land or a groove in accordance with the track pull-in enabling signal generated by the track pull-in enabling signal generating circuit, the header area signal generated by the header area signal generating circuit, and the track cross signal generated by the track cross signal generating circuit.
According to this invention, the header area signal generating circuit generates the header area signal, which shows the header area in the optical disk, in accordance with the track sum signal, which shows the total amount of reflected light of the optical beams with which the track, which has the land and the ground formed on the optical disc, is irradiated. The track pull-in enabling signal generating circuit generates the track pull-in enabling signal, which shows the track pull-in enabling timing, in accordance with the track error signal, which shows the shift from the track in the optical beams with which the optical disc is irradiated, the header area signal generated by the header area signal generating circuit. The track cross signal generating circuit generates the track cross signal, which shows that the optical beams with which the optical disc is irradiated have crossed the center of the track. The land/groove detection signal generating circuit generates the land/groove detection signal for determining a land or a groove in accordance with the track pull-in enabling signal generated by the track pull-in enabling signal generating circuit, the header area signal generated by the header area signal generating circuit, and the track cross signal generated by the track cross signal generating circuit. As a result, not only the track pull-in enabling timing but also the polarity of the land and that of the groove can be appropriately determined.